Audible alarms of various types are used for a wide variety of purposes. For example, it is common practice to employ backup alarms on commercial vehicles and mobile work machines to notify those in the vicinity that the vehicle or machine is moving and may be moving toward them. Typical alarms of this type may use a repeating audible signal, such as a beeping sound.
In crowded or congested areas, repeated use of audible alarms may become a source of irritation to those not close enough in proximity to be intended recipients of the alarm signals. The harshness of the alarm sound, although necessary in many environments, becomes objectionable beyond the immediate work area.
One attempt to minimize this source of irritation has been to use self-adjusting alarms; that is, alarms which monitor ambient sound and vary the amplitude of the alarm signal in response. Although the levels of the alarms may be reduced in lower noise areas, thus reducing perceived harshness to persons in the area, the varying amplitudes of the alarm signals tend to confuse those in the immediate work area. For example, a person may be near a moving vehicle or machine yet believe that the vehicle or machine is further away due to a reduced amplitude alarm signal.
In addition to the above issues, many work areas require multiple alarms for a multitude of vehicles and machines. Persons within these crowded work areas may, over time, begin to disregard the sound of an audible alarm since it is difficult to differentiate between several alarms repeatedly going off throughout the work site.
The present invention is directed to overcoming one or more of the problems as set forth above.